When I was a younger I absolutely ADORED the Megaman series. It was fast, fun and epic, especially the Megaman X and Zero games. Unfortunately Capcom has ruined any semblance of a decent plot by having too many chefs in the kitchen and the franchise now suffers from extreme sequelitis and sharkjumptis: The early games are worthwhile, the countless spinoffs and endless sequels are not.
The basic premise of every game is that you are a singular, lone robot up against an army of killer deathbots. You are armed with a pea blaster and skill alone. These games are daunting, but OH SO worthwhile tasks.
The original series, where the protagonist is the titular butler-bot turned war machine created by Dr. Light, is a light hearted collection of games where the recurring villain is a mad scientist named Dr. Wily who always has a both ridiculous and nefarious plot to take over the world. These games primarily were released on the NES and are fairly primitive by today’s 2D platformer standards, but are still worth playing. The cream of the crop is “Megaman and Bass,” which was oddly not released as “Megaman 9.” These old games are a retro blast from the early 1990’s era past.
Next there is Megaman X, which follows the story of Dr. Light’s final creation, X, and Dr. Wily’s final, badass, light saber wielding creation, Zero. These games, while they are still quite silly, are a major tonal shift from the original series. Gone are the ridiculous plots and in its place is a feeling of dread, AWESOME, and Wacky Robot Apocalypse. The main villain is a bald villain robot named Sigma who is even more persistent than Dr. Wily who plans to eliminate humans so robots can have the planet for their own. Unfortunately, only X1~4 are worth playing, with 4 just barely being enjoyable because you can play through the entire game as Zero.
Finally there is the Megaman Zero series, which for the most part only follows Zero’s story after the events of the X series. These games manage to recapture the spirit that the earlier games had that’s been lost in the mean time. This isn’t really surprising though, the Zero series was helmed by the original creator of Megaman. The Zero games take the Megaman and X gameplay formula and take it to the next level. Zero is fast, agile and ruthless in his capacity to destroy any opposing robot, all that is required is your skill. The first and the third games in this series are the best, with the second being decent and the fourth being abominable.
Of course, there are other Megaman games too, but most are only halfway decent (the ZX series, sequel to the Zero series) to horrible (Battle Network).